1. Field
The present disclosure is directed to a temperature-control device for stabilizing the temperature of electronics. The disclosure has particular utility in connection with controlling or minimizing condensation on electronic components that occurs due to frequent changes in atmospheric humidity experienced when traveling between different temperature/humidity regimes, e.g. as may be experienced in airplanes, and will be described in connection with such utility, although other utilities are contemplated.
2. Description of Related Art
Many commercial airplanes are equipped with an Auxiliary Power Unit (APU). The APU is controlled by the APU Engine Control Unit (ECU). Conventional ECU's are exposed to environmental conditions that could adversely affect reliability. In particular excessive condensation may form on components inside the ECU during the rapid transition between flight environmental conditions (cold/dry) to ground environmental conditions (warm/humid). The ECU is affected by the cold flight environment because it shuts down when the APU shuts down during flight and thus heat is not continuously generated. The environment surrounding the controller unit is known to reach temperatures in the 20° F. to 30° F. range. During flight, when the ECU is off, it is “cold soaked” by the air surrounding the unit. Upon landing, the typical operating procedure calls for the APU and ECU to be turned on and the airplane's cargo doors to be immediately opened by the ground crew to begin the unloading/loading process. If the outside air is warm and humid, the cold soaked ECU will cause condensation inside the unit which could result in both the ECU and APU) to be inoperative. This situation is similar to the phenomena often observed when a cold glass of ice water appears to “perspire” on a warm humid day.
It is believed that there are currently no “drop-in” solutions, i.e., solutions that solve the described problem without requalification. Below is a list of potential solutions that have been considered but rejected:    1) Warm air directed at the rack mounted electronic box using an additional fan, and heater. For this solution, two major system components (a fan and heater) are required. These two system components add power requirements and also require control methods that remove power in fault situations and give maintenance crews an indication that a fault has occurred (or conversely that the system has no faults).
2) Heater strips attached directly to or inside the rack mounted electronic box. Adding heater strips to or inside a rack-mounted electronic box also add power requirements and constitute a significant change that would require the rack mounted electronic box to be re-qualified which is not a practical solution. Re-qualification is a significant time and labor-intensive undertaking, and is to be avoided if possible.
3) Exercising the electronic box for the entire flight so that it generates heat continuously by leaving the APU running for the entire flight. The amount of fuel required to keep the APU running for the entire flight as well as the increased maintenance costs and reduction in life of the APU is cost prohibitive, especially with jet fuel prices escalating.
4) Exercising the electronic box for the entire flight so that it generates heat continuously by either internally modifying the electronic box or developing an external breakout box which simulates a normally running APU but allows the APU to remain off. Both an internal change to the rack mounted electronic box or a separate breakout box to simulate a functioning APU would be significant and require tremendous effort to design and qualify. Therefore, this solution is not considered practical.
5) Aircraft conditioned air, with a heater, blown into the general vicinity where a heat sensitive rack mounted electronic box is located. In certain aircraft operating modes conditioned air is often cold and can be moisture laden. For such modes solution 5) would have no value and could even exacerbate the problem. Further still, even for aircraft operating modes where warm air is supplied by the aircraft air conditioning system, this solution is not nearly as efficient as the proposed embodiments of the disclosure.
There exists a continuing need for a solution to the problem of condensation on sensitive electronics that are exposed to differing humidity/temperature regimes.